Media captionIslamic State's black flag has been seen above Kobane for the first time, reports Paul Adams

The key Syria-Turkey border town of Kobane might fall to Islamic State (IS) fighters soon, an official there has told the BBC.

A flag of Islamic State has been seen flying over a building on the eastern edge of Kobane.

The official, Idriss Nassan, confirmed IS was now in control of Mistenur, the strategic hill above the town.

Kobane has seen intense fighting over the past three days as Syrian Kurds try to defend the town.

The IS militants have been besieging it for nearly three weeks. Since then, more than 160,000 Syrians, mainly Kurds, have fled across the border.

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Another IS flag is seen on a hill overlooking the town, as the IS fighters take high ground

Capturing the town would give IS unbroken control of a long stretch of the Syrian-Turkish border.

In other developments on Monday:

At least 30 Kurdish fighters were killed in two attacks in the north-eastern Syrian city of Hassakeh, the Syrian Observatory for Human Rights monitoring group said

The US Central Command confirmed a fresh air strike by US-led forces "destroyed two IS fighting positions south of Kobane"; there were two other air strikes in Syria and three in Iraq over Sunday and Monday, it said

Nato Secretary-General Jens Stoltenberg vowed to protect Turkey, a member state, saying: "Turkey should know that Nato will be there if there is any spillover, any attacks on Turkey as a consequence of the violence we see in Syria"

Civilian evacuation

The BBC's Paul Adams, near the border, says this has been a long day of constant gunfire, with smoke drifting across the rooftops of Kobane and occasional thunderous explosions reverberating across the valley.

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Turkish forces are stationed on a hill close to Kobane

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Kurds angry with Turkey's role have clashed with Turkish forces

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The IS offensive has forced tens of thousands to flee over the border into Turkey

He says the street fighting has begun and that this feels like the beginning of the end.

A steady stream of Turkish ambulances has been racing to and fro, our correspondent says, and it is now being reported that a mass evacuation of civilians is under way.

Mr Nassan told the BBC there were still thousands of civilians in Kobane.

He said IS was now in control of Mistenur and that, in theory, gave the attackers a huge strategic advantage. But Mr Nassan said IS was not yet firing down into the town from the hill.

He said there was shelling in all parts of Kobane, adding: "Yes, it will certainly fall soon."

Mr Nassan could not say how long this would take, but added: "I'm not going to give up my home and my country easily."

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Media captionPaul Adams and his team were filming when they were attacked by Turkish police trying to clear the border area

Esmat al-Sheikh, head of the Kobane Defence Authority, told Reuters news agency: "If they enter, it will be a graveyard for us and for them. We either win or die. We will resist to the end."

On Sunday a Kurdish woman in Kobane killed a number of IS fighters in a suicide bomb attack, Kurdish sources said.

Turkish Kurds and refugees have clashed with Turkish security forces on the border for the past two days.

They are angry and disappointed at Turkey's perceived inaction over IS in recent months, as well as its refusal to allow them to cross into Syria to fight.

Last week, Turkey pledged to prevent Kobane from falling to the militants and its parliament authorised military operations against militants in Iraq and Syria.

But it appears to have taken no action so far to prevent the fighting.

Correspondents says Turkey is reluctant to lend support to the Kurdish forces in the town because they are allied to the PKK, banned as a terrorist organisation in Turkey.

KOBANE KEY FACTS:

Kobane, known in Arabic as Ayn al-Arab, and the villages surrounding it were home to about 400,000 people, most of them Kurds

Kurdish parties have governed the area since the Syrian army withdrew two years ago

In the first half of 2013, IS seized control of neighbouring areas, leaving Kobane surrounded on three sides

IS launched a major offensive on 16 September, prompting more than 100,000 people to flee to Turkey